Three-dimensional semiconductor packages become essential for a higher density and capacity. The 3D semiconductor packaging technology is by thinning semiconductor chips, and stacking them in multilayer structure while providing through-silicon via (TSV) interconnects. Fabrication of such packages requires the steps of thinning a substrate having a semiconductor circuit formed therein by grinding its non-circuit forming surface or back surface, and forming TSV and electrodes on the back surface. In the prior art, prior to the step of grinding the back surface of a silicon substrate, a protective tape is attached to the surface of the substrate opposite to the surface to be ground for preventing the wafer from breakage during the grinding step. Since the protective tape is based on an organic resin film, it is flexible, but has insufficient strength and heat resistance to withstand the TSV forming step and the step of forming interconnects on the back surface.
It is then proposed to bond a semiconductor substrate to a support of silicon or glass, for example, via an adhesive layer. The resulting system is sufficient to withstand the steps of grinding the back surface and forming TSV and electrodes on the back surface. The adhesive layer for bonding the substrate to the support is critical for this system. The adhesive layer must bond the substrate to the support without leaving gaps, be durable enough to withstand the subsequent steps, and eventually allow the thin wafer to be readily released from the support. The adhesive layer is referred herein to as “temporary adhesive layer” since it is finally removed.
With regard to temporary adhesive layers and removal thereof, Patent Document 1 discloses a layer of an adhesive composition containing a light absorbing agent. The adhesive layer is irradiated with high intensity light for decomposing the adhesive composition so that the layer may be removed. Patent Document 2 discloses a layer of an adhesive composition comprising a heat melting hydrocarbon compound, wherein the layer can be bonded and released in the heat molten condition. The former technology requires an expensive tool such as laser, a particular substrate (typically glass substrate) that is transmissive to laser light as the support, and a longer time of treatment per substrate. The latter technology is simple because of control only by heat, but is applicable to a limited range because of instability at high temperatures in excess of 200° C. These temporary adhesive layers are not adequate to form a layer of uniform thickness on a heavily stepped substrate and to provide a complete bond to the support.
Patent Document 3 discloses the use of a silicone pressure-sensitive adhesive composition as the temporary adhesive layer. A substrate is bonded to a support with an addition reaction curable silicone adhesive composition. On removal, the assembly is immersed in an etching solution capable of dissolving or decomposing the silicone resin, whereby the substrate is separated from the support. This method takes a very long time for removal and is applicable to the commercial manufacture process with difficulty.